Light action control is one of may facets of timing and program control technology. Special fade-in, fade-out and dwell lighting effects for signs, displays, exhibits, wherever a variable-speed, multiple-circuit timer can serve to control the lights of theater marquees, window displays and trade show exhibits, use the hypnotic effect of light-in-motion to lure customers, to attract visitors to a convention booth, or to draw attention to the sales message of an advertising sign.
These exhibit-displays, when used in the chaser mode, have been controlled in the past by electromechanical timers which are motor-driven and have cam-actuated, heavy silver electrical contacts which bounce, stick and wear out. They are expensive, explosion-prone and offer no protection against large lamp in-rush currents following lamp switch-on. Switching by electromechanical timers is invariably hard on bulbs.
The subject matter of the present invention concerns switching of light bulbs in A.C. circuits. Switch-on and switch-off control of light bulbs is to be distinguished from fade-in and fade-out control of the same which concerns those special lighting effects, individually custom-suited to fit any one particular requirement. For example, theaters and night clubs use dimmers to fade out house lights and fade in footlights, spotlights or stage lights. Dimmers are blended to synchronize light with motion and sound.
Uncontrolled switch-on and switch-off of lamp by electromechanical or solid state means, regardless of the voltage amplitude being applied to the lamp at that instant, can be damaging to lamp life if done at or near A.C. peak voltage on a repetitive basis. For this reason, lamp-driving circuits for light chasers, etc., have expensive zero-voltage crossover detection circuitry and triggering devices to produce soft switching.
There is presently a need for a low-cost solid state timer-stepper which provides for soft-switching control of the triacs and isolation of the control logic from A.C. line or triac transient, and which in a light-chaser application produces a special "ripple" lighting effect.